It is the purpose of this project to measure the effect of polycyclic hydrocarbons on the microsomal enzymes of macrophages and lymphocytes. The areas investigated have been: (1) development and standardization of an assay for aryl-hydrocarbon hydroxylase AHH) in human peripheral blood monocytes; (2) to measure the effect of polycyclic hydrocarbons in guinea pig lymphoid tissue; (3) to find whether interaction of polycyclic hydrocarbons with macrophages facilitates induction or expression of contact hypersensitivity; and (4) to evaluate levels of inducible AHH activity in monocytes from normal humans and patients with lung cancer.